Question

Calculate the standard enthalpy of formation of CH₃OH_(l) from the following data: 

Answer 1

The reaction that takes place during the formation of CH₃OH_(l) can be written as: 

C_(s) + 2H₂O_(g) +           CH₃OH_(l) (1) 

The reaction (1) can be obtained from the given reactions by following the algebraic calculations as: 

Equation (ii) + 2 × equation (iii) – equation (i) 

∆_fH^θ [CH₃OH_(l)] = ∆cH^θ + 2∆fH^θ [H₂O_(l)] – ∆rH^θ 

= (–393 kJ mol^–1 ) + 2(–286 kJ mo^_l–1 ) – (–726 kJ mol^–1 ) 

= (–393 – 572 + 726) kJ mo^_l–1 

∆_fH^θ [CH₃OH_(l)] = –239 kJ mol^–1